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    <title>Document</title>
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<body>
    <script>
        function add(num) {
            var count = num;
            var _b = function (l) {
                count += l;
                return _b
            }
            _b.valueOf = function () {
                return count
            }
            return _b
        }
        var c = add(1)(2)(3);
        console.log(c)    //6
    </script>
</body>

</html>